Method for the detoxification of exhaust gases of internal combustion engines

ABSTRACT

Exhaust gases of internal combustion engines are detoxified by a method in which they are passed first through an after burner, and then through a catalyzer. Burning in the after burner to remove hydrocarbons and carbon monoxide is limited so that enough carbon monoxide remains to react with nitrogen oxides in the catalyzer.

United States Patent 1191 a CARBURATOR l ENGINE [AFTER BURNER 3 4 5 11] 3,803,839 Santiago 5] Apr. 16, 1974 [54] METHOD FOR THE DETOXIFICATION OF 3,738,341 6/1973 Loos 60/285 X S G S S OF INTERNAL 3,406,515 10/1968 Behrens 60/305 3,524,721 8/1970 Stephens.... 23/2 E COMBUSTION ENGINES 3,565,574 1 2/1971 Kearby 60/301 [75] 1 Inventor: Andres Santiago, Augsburg, 3,581,490 6/1971 Morris 60/286 Germany 3,599,427 8/1971 Jones 60/274 [73] Assignee: Zeuna-Staerker KG, Augsburg,

Germany Primary Examiner-Douglas Hart [22] Filed: Sept. ,13, 1971 Attome A cut, or Firm-W. G. Fasse y 8 [21] Appl. No.: 179,678

[30] Foreign Application Priority Data ABSTRACT Sept. 12, 1970 Germany 2045233 52 us. Cl 60/274, 60/289, 60/301, Exhaust gases of internal combustion engines are 2 2 3 7 toxified by a method in which they are passed first 51 Int. Cl. F0ln 3/16 through an after burner, and through a catalyzer- [58 Field of Search 60/274, 301, 289; 23/2 E, Burning in the after burner to remove hydrocarbons 3 7 288 423/213] and carbon monoxide is limited so that enough carbon monoxide remains to react with nitrogen oxides in the [56] References Cited cataly UNITED STATES PATENTS 3,730,157 5/1973 Gerhold 60/285 4 Claims, 1 Drawing Figure EXHAUST MANlFOLD MUFFLER 8 CARBURATOR I ENGINE EXHAUST MANIFOLD AFTER BURNER 7 3 4 5 6 CATALYZER MUFFLER INyENToR ANDRES SANTIAGO ATTORNEY METHOD FOR THE DETOXIFICATION OF EXHAUST CASES OF INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION This invention relates to a method for the detoxification of the exhaust gases of internal combustion engines, especially vehicular engines, by reducing the vol- 1 ume of hydrocarbons, carbon monoxide and nitrogen oxide in the exhaust gas, so that the proportions of the hydrocarbons and carbon monoxide exhaust gas components are first reduced by oxidation in an after burning device, and subsequently the exhaust gas is fed through a catalyzer for an after reaction.

In the past, detoxification devices have been provided for reducing the above mentioned three exhaust gas components to such an extent that a danger of contaminating the air is substantially reduced or eliminated.

One well known method suggests detoxification of the exhaust gases in two steps. In the first step, the exhaust gas if fed through an after burning device in which the hydrocarbons and carbon monoxide are proportionally reduced. However, as is known, it is not possible to reduce the proportion of the nitrogen oxides in such afterburning devices. The reduction of the proportion of the nitrogen oxideis accomplished, in accordance with the known method, by a feedback of the exhaust gases, whereby the feedback apparatus is com bined with the after burning device. The exhaust gas feedback is accomplished in accordance with the known method by syphoning off a portion of the exhaust gas from the exhaust gas pipe upstream of the muffler and supplying it to the carburator. In this manner the combustion temperature is reduced to such an extent that substantially less nitrogen oxide is produced in the engine during combustion. I

The above described prior art method has the disadvantage that it is rather costly, because the feedback and the metering of the exhaust gases requires additional control means such as measuring shutters, valves, as well as filters and so forth.

In another known method the ignition timing is shifted to reduce the proportion of nitrogen oxide in the exhaust gases. This method also reduces the combustion temperature in theengine, as in the case of the exhaust feedback method. This method, however, has the substantial disadvantage that it results in a significant increase in fuel consumption.

In both of the above methods for reducing the production of nitrogen oxide the disadvantage arises that the reduction of the combustion temperature effects an increase in the proportion of hydrocarbons in the exhaust gas, consequently, additional steps are necessary for removing the increased proportion of hydrocarbon.

According to another known arrangement as disclosed for example in German Pat. No. 1,292,146, a catalyzer is provided downstream of the after burning device. The combustion in the after burning device is controlled so that the hydrocarbons and the carbon monoxide are burned as completely as possible in the after burner. This is accomplished by applying a corresponding excess of air to the after burner. The additional air supplied to the after burner may be preheated if desired.

In this arrangement the catalyzer serves the function of burning the hydrocarbons from the after burner which were not burned in the after burner, whereby the proportion of nitrogen oxide in the exhaust gas is supposed to be regulated. However, in such an after burning in the catalyzer wherein an excess of air is employed, there is the danger of forming toxic nitrogen dioxides.

OBJECTS OF THE INVENTION In view of 'the above disadvantages of the known methods, it is the object of this invention to provide an improved method of the type last described above, that is a method which employs an after burning device with a following catalyzer in which a substantial elimination of the three mentioned toxic exhaust gas components is possible without an undesirable power loss.

It is yet another object to eliminate the above mentioned toxic components of internal combustion engine exhaust gases by reacting these components, or at least certain of these components with each other so that compounds will result which are not harmful.

' DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT:

In order that the invention may be clearly understood, it will now be described by way of example, with reference to the single FIGURE of the accompanying drawing which illustrates schematically an exhaust system of an internal combustion engine which may be employed for performing the method of the invention.

A conventional engine 1 is provided with an exhaust manifold 2 connected to an after burner 3 which as such is of conventional construction. The outlet of the after burner 3 is connected to a catalyzer 4. The outlet of the catalyzer 4 is connected to an exhaust gas conduit 5 and thence to a conventional muffler 6 if desired.

In the method according to the invention, the regulation or control of the oxygen supply in the system is essential. The proportion of oxygen which is desirable for thevoxidation in the afterbumer device, can be obtained in the simplest fashion by controlling the air supply. This may be done in a practical manner by supplying just enough air to the after burner device 3 to oxidize the necessary proportion of the carbon monoxide and to burn the proportion of the hydrocarbons present so that a complete combustion of the carbon monoxides in the after burner is avoided. The air supply may for example be accomplished by blowing fresh air into the exhaust pipes upstream of the after burner device for example by means of a suitably controlled blower 9 connected by pipe 7 to the upstream side of after burner 3. Alternatively the necessary additional air may be provided by a suitable selection of the fuel air mixture by correspondingly tuning or adjusting the carburator 8. These two techniques may also be combined.

When the method according to the invention is employed, the hydrocarbons in the exhaust gas are completely oxidized in the after burner device 3, except for an insignificant remainder, so that carbon dioxide and water are formed. The desired oxidation may be achieved by a suitable control of the temperature in the after burner 3, as well as by a suitable conduction of the exhaust gas inside the after burner. Only the carbon monoxide and the nitrogen oxide are involved in the following reduction process in the catalyzer. In this regard it must be assured that the oxygen proportion in the catalyzer does not exceed the limits which, if exceeded, would result in the formation of harmful nitrogen oxide which would remain in the exhaust gas reaching the atmosphere.

Suitable catalyzing materials or catalysts for use in the method according to the invention are readily available and are well known to those skilled in the art. It is preferable to employ granular metal oxides for the catalysts, the grains of which have large surface areas.

The optimum detoxification is accomplished in accordance with the invention by passing the entire quantity of exhaust gas through the after burner 3 as well as through the catalyzer 4.

According to a modification of the invention the after burner device and the catalyzer may be combined in a unitary structure. As an example some components of the after burner device may be coated with the catalyst material, such as those components which are subject to especially heavy wear and therefore are subject to occasional replacement.

In the following paragraphs the functional sequence of the method according to the invention will be explained with reference to the exhaust gas components of interest.

The exhaust gas emanating from the motor, that is, the exhaust gas which is not yet detoxified comprises generally about 4 per cent by volume of carbon monoxide, 0.06 per cent by volume of hydrocarbons and 0.12 per cent by volume of nitrogen oxide The hydrocarbons are removed substantially completely by oxidation in the after burner device (actually a remainder of about 30 X per cent by volume remains) and the carbon monoxide is removed to the extent that per cent by volume remains. The following basic reactions occur in the after burner:

In the catalyzer which follows the after burner device the 1.5 per cent by volume of carbon monoxide reacts with 0.12 per cent by volume of nitrogen oxide, so that carbon dioxide and nitrogen are formed, whereby only an insignificantly small amount of 0.3 per cent by volume of carbon monoxide remains in the gas to be eventually exhausted. The reduction in the catalyzer takes place in accordance with the following basic equation:

CO+NO CO +N Heretofore those skilled in the art believed that for a substantial and efficient detoxification of the exhaust gases it was desirable to completely burn the exhaust gases in the after burner, and that therefore a correspondingly large quantity of secondary air must be supplied to the after burner. Contrary thereto, the invention is based upon recognition of the fact that, for a detoxification which is as efficient as possible, it is essential that a certain proportion of the carbon monoxide remains in the exhaust gas, so that the necessary amount of carbon monoxide is available for reduction of the nitrogen oxides in the catalyzer located downstream of the after burner.

In an especially, advantageous operating condition of the present invention, the carbon monoxide is oxidized in the after burner to such an extent that the reaction in the catalyzer occurs as a reduction in the presence of not more than about 0.5 to 0.8 per cent by volume of oxygen.

In comparison with known methods which employ after burning in combination with a catalyzer, the present invention achieves a more complete removal of the toxic agents from the exhaust gas as italso removes the nitrogen oxides. This result is possible since the combustion in the engine occurs at normal combustion temperatures. The proportions of hydrocarbons and carbon monoxide in the exhaust gas which are produced by the engine may now be oxidized as completely as necessary in an after burner device 3 of conventional construction. The substantially complete removal of the nitrogen oxides is accomplished according to the invention, by regulating the proportion between the amount of carbon monoxide which remains in the exhaust gas after the passage of the after burning device and the amount of nitrogen oxides remaining after the combustion in the engine. The proportion is controlled substantially in accordance with stoichiomctric proportional quantities, having due regard to the reaction in the catalyzer.

According to the teaching of the present invention, then, just as much-carbon monoxide should remain in the after burner device as is stoichiometrically suffcient for a complete reduction of the nitrogen-oxygen compounds in the catalyzer. The hydrocarbons are preferably completely oxidized in the after burner device. However, it is also permissible that small residual amounts of hydrocarbons and/or a small excess of carbon monoxide may be present in the catalyzer where they are oxidized to produce carbon dioxide and water.

In such instances, the catalyzer or catalyst may be selected so that the reduction of the nitrogen oxides as well as the oxidation of the hydrocarbon compounds to carbon dioxide and water in the catalyzer are facilitated. Such catalysts are well'known.

The method according to the invention does not impair the efficiency of combustion in the engine. However, a certain power output reduction will result due to the use of a catalyzer. As compared with previously employed methods, the method of the invention attains a higher degree of detoxification with regard to the three harmful exhaust gas components discussed above.

Incidentally, it has been found that the above mentioned granular metal oxide catalysts could, for example be oxides of metals such as chromium, manganese, iron, cobalt, nickel, copper, silver, and platinum. Naturally, the latter two examples will be used exceptionally in view of price considerations. Moreover, the granular oxides of any one of these metals may be mixed with any other for the present purposes, and the listed examples do not exclude the use of other suitable catalysts.

SUMMARY OF THE INVENTION According to the method of the present invention, the volume proportion of the carbon monoxide in the exhaust gas is reduced in the after burner device only to such an extent that it corresponds to about ten times or slightly more than ten times the volume proportion of the nitrogen oxide in the exhaust gas, thereafter the exhaust components in these proportions are reacted in a catalyzer to form carbon dioxide and nitrogen.

Although the invention has been described with reference to specific example embodiments, it is to be understood that it is intended to cover all modifications and equivalents within the scope of the appended claims.

What I claim is:

1. In a method of operating an internal combustion engine having an exhaust outlet for detoxifying the exhaust gases of said internalcombustion engine by diminishing the volume proportions of hydrocarbons, carbon monoxide and nitrogen oxide in the exhaust gas, wherein in a first step the proportions of hydrocarbons and carbon monoxide in the exhaust gas are diminished by oxidation in an after burner device and wherein in a second step the exhaust gas is fed to a catalyzer for an after reaction, the improvement comprising supplying by controllable air supply means to a point downstream of said engine exhaust outlet an air volume sufficient for partially diminishing in said first oxidation step in said after burner the volume proportion of the carbon monoxide in the exhaust gas to such an extent that the remainder of carbon monoxide corresponds to about 10 times the volume proportion of the nitrogen oxide in the exhaust gas, and thereafter reacting these proportions of about 10 parts by volume of carbon monoxide and 1 part by volume of nitrogen oxide, said proportioning of CO to NO amounting to substantially stoichiometric proportions in said catalyzer, with each other in said catalyzer to form carbon dioxide and nitrogen by reduction of the nitrogen oxide to nitrogen and further oxidizing the remaining carbon monoxide to carbon dioxide: thus C0 NO CO N.

2. The method according to claim 1, wherein for said reduction sufficient air is supplied so that the reduction in the catalyzer takes place in the presence of about 0.5 to 0.8 percent by volume of oxygen.

3. The method according to claim 2, comprising passing all of the exhaust gas of the engine first through an after burner device and then through a catalyzer.

4. The method of claim 1, wherein said step of oxidizing comprises supplying air to said after burner in an amount sufficient to substantially completely oxidize said hydrocarbons in said after burner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3.803.839 Dated April 16, 1974 Inventor(s) dr s Santiago 'It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column}, line 37 "30 x 10' v r I v 4 should be Signed and sealed this 17th day of September 1974,,

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer 7 Commissioner of Patents FOR 0 USCOMM-DC 60376-P69 U S GOVERNMENY PRINTING OFFICE 1959 0-366-334. 

1. In a method of operating an internal combustion engine having an exhaust outlet for detoxifying the exhaust gases of said internal combustion engine by diminishing the volume proportions of hydrocarbons, carbon monoxide and nitrogen oxide in the exhaust gas, wherein in a first step the proportions of hydrocarbons and carbon monoxide in the exhaust gas are diminished by oxidation in an after burner device and wherein in a second step the exhaust gas is fed to a catalyzer for an after reaction, the improvement comprising supplying by controllable air supply means to a point downstream of said engine exhaust outlet an air volume sufficient for partially diminishing in said first oxidation step in said after burner the volume proportion of the carbon monoxide in the exhaust gas to such an extent that the remainder of carbon monoxide corresponds to about 10 times the volume proportion of the nitrogen oxide in the exhaust gas, and thereafter reacting these proportions of about 10 parts by volume of carbon monoxide and 1 part by volume of nitrogen oxide, said proportioning of CO to NO amounting to substantially stoichiometric proportions in said catalyzer, with each other in said catalyzer to form carbon dioxide and nitrogen by reduction of the nitrogen oxide to nitrogen and further oxidizing the remaining carbon monoxide to carbon dioxide: thus CO + NO -> CO2 + N.
 2. The method according to claim 1, wherein for said reduction sufficient air is supplied so that the reduction in the catalyzer takes place in the presence of about 0.5 to 0.8 percent by volume of oxygen.
 3. The method according to claim 2, comprising passing all of the exhaust gas of the engine first through an after burner device and then through a catalyzer.
 4. The method of claim 1, wherein said step of oxidizing comprises supplying air to said after burner in an amount sufficient to substantially completely oxidize said hydrocarbons in said after burner. 